It combines a disconnect switch, a thermal overload relay, and a magnetic short-circuit release in one package, sized to protect a motor against overload, phase failure, and short circuit. That's fast enough to keep the windings from cooking on a stalled rotor but slow enough to let the motor accelerate normally under load.
Breaking capacity — the real-world number
Any mounting position is allowed, which helps when you're fitting it into a tight corner of an existing panel. The 70 mm width and 176 mm depth are the numbers to check for gland-plate clearance and door-swing interference. That's one less relay to wire and one less thing to fail out here in the grease.